Add unique index for fields_hash when not deleted

db/migrate/20250507183451_add_partial_unique_index_to_heartbeat_fields_hash.rb

@@ -0,0 +1,9 @@
+class AddPartialUniqueIndexToHeartbeatFieldsHash < ActiveRecord::Migration[8.0]
+  def change
+    # Add a partial index that only applies to non-deleted records
+    add_index :heartbeats, :fields_hash,
+              unique: true,
+              where: "deleted_at IS NULL",
+              name: "index_heartbeats_on_fields_hash_when_not_deleted"
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_05_07_182617) do
+ActiveRecord::Schema[8.0].define(version: 2025_05_07_183451) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -210,6 +210,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_05_07_182617) do
     t.datetime "deleted_at"
     t.index ["category", "time"], name: "index_heartbeats_on_category_and_time"
     t.index ["fields_hash"], name: "index_heartbeats_on_fields_hash", unique: true
+    t.index ["fields_hash"], name: "index_heartbeats_on_fields_hash_when_not_deleted", unique: true, where: "(deleted_at IS NULL)"
     t.index ["user_id"], name: "index_heartbeats_on_user_id"
   end